Toxic effects of chlorpyrifos on biochemical composition, enzyme activity and gill surface ultrastructure of three species of small fishes from India.

The effects of chlorpyrifos, a frequently detected organophosphate in aquatic ecosystems, on biochemical (protein and glycogen) contents and oxidative enzyme activities (catalase and lipid peroxidation) in liver, muscle and gill tissues of three freshwater fish Trichogaster fasciata, Mystus vittatus and Heteropneustes fossilis were evaluated after 21-day exposure to 1 and 10% of 96 h LC₅₀ of this pesticide, which were 1.63 and 16.3 µg L^-1; 5.87 and 58.7 µg L^-1 and 2.12 and 21.2 µg L^-1, respectively. On comparing with control, significant reductions in protein concentration were found in liver, muscle and gill of the three fishes treated with both higher as well as lower concentrations of the pesticide except in gill of M. vittatus and liver of H. fossilis treated with the lower concentrations. Glycogen content reductions were significant in the liver and muscle of the fishes, as well as gill tissue of T. fasciata treated with the two pesticide concentrations. Significant elevations of catalase activity were found in liver of the three fishes treated with the higher concentrations, in muscle tissues of both T. fasciata and M. vittatus treated with both the concentrations and in gills of the three fishes except H. fossilis treated with the lower concentration of the pesticide. Significant elevations of lipid peroxidation level were also found in liver of all the three fish species treated with the higher concentrations, in the muscle tissue of M. vittatus as well as in the gill of T. fasciata and H. fossilis treated with both the concentrations of the pesticide. Chlorpyrifos exposed gill ultrastructure of T. fasciata, M. vittatus and H. fossilis revealed concentration-dependent effects of the pesticide on gill surface ultrastructure which include distortion of primary and secondary lamellae, deterioration of pavement cell and microridge structures, extrusion of red blood cells (RBCs), secretion of mucous layer on filament, sloughing of primary lamellae and clumping of secondary lamellae. The present study parameters could serve as useful biomarkers for evaluating the risk of pesticide toxicity to fish. These findings also point out the possible health risks to the consumers of these fish captured from contaminated water bodies.